The long-term objective of this project is to elucidate certain aspects of the dynamics of phase separation. The proposed research will consider the separation of anhydrous cholesterol crystals from solutions which model, to some degree, biological systems. Three specific aims of the proposed work are to investigate the effect of: (1) molecular aggregation in the one-phase region on phase separation, (2) degree of supersaturation on initial rates of crystal growth, and (3) ionic strength of solvent on molecular aggregation and crystal growth. Solutions will be studied in the one-phase region where cholesterol forms molecular aggregates, using infrared and ultraviolet spectroscopy. The effect of temperature and ionic strength on the short-range structure of the liquid state will be studied as the solution approaches the limit of practical supersaturation. The scattering of light just above the temperature of phase separation may give some insight to fluctuations in the one-phase region responsible for nucleation of the new phase; similar studies in the two-phase region will probe the early stages of phase separation. Optical studies of crystal growth allow a measurement of crystal growth and size distribution under various conditions of interest. The insignificance of the proposed research may be viewed in terms of its contribution to the basic understanding of the dynamics of phase separation, as well as to the understanding of lipid deposition in biological systems. The project will involve studies of the basic physical process, phase separation, in what may serve as model biological systems. The results of the studies will provide potentially important information to the understanding and control of cholestrol-based diseases of the body.